1. Field of the Invention
This invention relates generally to a method for putting a fuel cell system on a vehicle in a performance mode and, more particularly, to a method for preloading certain vehicle sub-systems in a fuel cell system so as to increase vehicle performance when high power is requested.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. A hydrogen fuel cell is an electro-chemical device that includes an anode and a cathode with an electrolyte therebetween. The anode receives hydrogen gas and the cathode receives oxygen or air. The hydrogen gas is dissociated in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The protons react with the oxygen and the electrons in the cathode to generate water. The electrons from the anode cannot pass through the electrolyte, and thus are directed through a load to perform work before being sent to the cathode.
Proton exchange membrane fuel cells (PEMFC) are a popular fuel cell for vehicles. The PEMFC generally includes a solid polymer electrolyte proton conducting membrane, such as a perfluorosulfonic acid membrane. The anode and cathode typically include finely divided catalytic particles, usually platinum (Pt), supported on carbon particles and mixed with an ionomer. The catalytic mixture is deposited on opposing sides of the membrane. The combination of the anode catalytic mixture, the cathode catalytic mixture and the membrane define a membrane electrode assembly (MEA).
Several fuel cells are typically combined in a fuel cell stack to generate the desired power. The fuel cell stack receives a cathode reactant gas, typically a flow of air forced through the stack by a compressor. Not all of the oxygen is consumed by the stack and some of the air is output as a cathode exhaust gas that may include water as a stack by-product. The fuel cell stack also receives an anode hydrogen reactant gas that flows into the anode side of the stack. The stack also includes flow channels through which a cooling fluid flows.
For certain vehicle operation, it is desirable that the vehicle provide high performance by minimizing the throttle response time, i.e., the time from when the vehicle operator requests power from the fuel cell stack to when the fuel cell stack is able to deliver the power. As is well understood in the art, there is a certain lag between when power is requested from the fuel cell stack in a fuel cell system until when the fuel cell stack is able to deliver the power. For example, the compressor that provides the cathode air to the cathode side of the fuel cell stack is limited in its ability to immediately provide enough air when high power is commanded from the fuel cell stack. Not only is there an inherent lag time while the compressor spools up to the desired speed, the power from the fuel cell stack is also selectively distributed between the traction system of the vehicle and the compressor to provide the cathode air. Therefore, it may be desirable to incorporate techniques for increasing fuel cell vehicle performance in response to a high power request.